Curl
late Middle English: from obsolete crulle ‘curly’, from Middle Dutch krul .
wiktionary
From metathesis of Middle English crulle(“curled, curly”), from Middle Dutch crul, crulle(“curl”), ultimately from Proto-Germanic *kruzlǭ(“bent or crooked object, curl”), of unknown origin.
Cognate with Saterland Frisian Krulle(“curl, lock”), West Frisian krul(“curl”), Dutch krul(“curl”), German Low German Krull(“curl”), dialectal German Krolle(“curl”), Danish krølle(“curl”), Norwegian krull(“curl”). Related also to Saterland Frisian Kruus(“curl”), German kraus(“frizzy, crumpled, curly”), Swedish krusa(“to crimp, curl”). Compare also Gothic 𐌺𐍂𐌹𐌿𐍃𐍄𐌰𐌽( kriustan, “to grind, crush, gnash”).
etymonline
curl (v.)
late 14c. (implied in curled), "turn, bend, form in ringlets" (transitive), a metathesized formation corresponding to the Middle English adjective crull, crulle (c. 1300), which is probably from an unrecorded Old English word or from Middle Dutch krul "curly," from Proto-Germanic *krusl- (source also of East Frisian krull "lock of hair," Middle High German krol, Norwegian krull, Danish krølle "curl").
Intransitive sense of "take the form of a curl, assume a spiral shape" is from 1520s (originally of hair). Meaning "to play at curling" is from 1715. Related: Curled; curling.
curl (n.)
c. 1600, "a ringlet of hair;" by 1610s in reference to anything of similar spiral or undulating form; from curl (v.). Surfer slang for "curved top of a breaking wave" is by 1962.
